[PATCH 1/8] perf/x86: Add msr probe interface

[Jiri Olsa]

Adding perf_msr_probe function to provide interface for
checking up on MSR register and set the related attribute
group visibility.

User defines following struct for each MSR register:

  struct perf_msr {
       u64                       msr;
       struct attribute_group   *grp;
       bool                    (*test)(int idx, void *data);
       bool                      no_check;
  };

Where:
  msr      - is the MSR address
  attrs    - is attribute groups array to add if the check passed
  test     - is test function pointer
  no_check - is bool that bypass the check and adds the
              attribute without any test

The array of struct perf_msr is passed into:

  perf_msr_probe(struct perf_msr *msr, int cnt, bool zero, void *data)

Together with:
  cnt  - which is the number of struct msr array elements
  data - which is user pointer passed to the test function
  zero - allow counters that returns zero on rdmsr

The perf_msr_probe will executed test code, read the MSR and
check the value is != 0. If all these tests pass, related
attribute group is kept visible.

Also adding PMU_EVENT_GROUP macro helper to define attribute
group for single attribute. It will be used in following patches.

Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
 arch/x86/events/Makefile |  2 +-
 arch/x86/events/probe.c  | 45 ++++++++++++++++++++++++++++++++++++++++
 arch/x86/events/probe.h  | 29 ++++++++++++++++++++++++++
 3 files changed, 75 insertions(+), 1 deletion(-)
 create mode 100644 arch/x86/events/probe.c
 create mode 100644 arch/x86/events/probe.h

diff --git a/arch/x86/events/Makefile b/arch/x86/events/Makefile
index b8ccdb5c9244..ec29a466444a 100644
--- a/arch/x86/events/Makefile
+++ b/arch/x86/events/Makefile
@@ -1,4 +1,4 @@
-obj-y					+= core.o
+obj-y					+= core.o probe.o
 obj-y					+= amd/
 obj-$(CONFIG_X86_LOCAL_APIC)            += msr.o
 obj-$(CONFIG_CPU_SUP_INTEL)		+= intel/
diff --git a/arch/x86/events/probe.c b/arch/x86/events/probe.c
new file mode 100644
index 000000000000..c2ede2f3b277
--- /dev/null
+++ b/arch/x86/events/probe.c
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/export.h>
+#include <linux/types.h>
+#include <linux/bits.h>
+#include "probe.h"
+
+static umode_t
+not_visible(struct kobject *kobj, struct attribute *attr, int i)
+{
+	return 0;
+}
+
+unsigned long
+perf_msr_probe(struct perf_msr *msr, int cnt, bool zero, void *data)
+{
+	unsigned long avail = 0;
+	unsigned int bit;
+	u64 val;
+
+	if (cnt >= BITS_PER_LONG)
+		return 0;
+
+	for (bit = 0; bit < cnt; bit++) {
+		if (!msr[bit].no_check) {
+			struct attribute_group *grp = msr[bit].grp;
+
+			grp->is_visible = not_visible;
+
+			if (msr[bit].test && !msr[bit].test(bit, data))
+				continue;
+			/* Virt sucks; you cannot tell if a R/O MSR is present :/ */
+			if (rdmsrl_safe(msr[bit].msr, &val))
+				continue;
+			/* Disable zero counters if requested. */
+			if (!zero && !val)
+				continue;
+
+			grp->is_visible = NULL;
+		}
+		avail |= BIT(bit);
+	}
+
+	return avail;
+}
+EXPORT_SYMBOL_GPL(perf_msr_probe);
diff --git a/arch/x86/events/probe.h b/arch/x86/events/probe.h
new file mode 100644
index 000000000000..4c8e0afc5fb5
--- /dev/null
+++ b/arch/x86/events/probe.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ARCH_X86_EVENTS_PROBE_H__
+#define __ARCH_X86_EVENTS_PROBE_H__
+#include <linux/sysfs.h>
+
+struct perf_msr {
+	u64			  msr;
+	struct attribute_group	 *grp;
+	bool			(*test)(int idx, void *data);
+	bool			  no_check;
+};
+
+unsigned long
+perf_msr_probe(struct perf_msr *msr, int cnt, bool no_zero, void *data);
+
+#define __PMU_EVENT_GROUP(_name)			\
+static struct attribute *attrs_##_name[] = {		\
+	&attr_##_name.attr.attr,			\
+	NULL,						\
+}
+
+#define PMU_EVENT_GROUP(_grp, _name)			\
+__PMU_EVENT_GROUP(_name);				\
+static struct attribute_group group_##_name = {		\
+	.name  = #_grp,					\
+	.attrs = attrs_##_name,				\
+}
+
+#endif /* __ARCH_X86_EVENTS_PROBE_H__ */
-- 
2.21.0